Display device

ABSTRACT

There is disclosed a display device designed to cut off noise to prevent the surroundings from being adversely affected by noise. The display device has a circuit board on which a support frame is mounted in a given position. A liquid crystal panel is mounted on the support frame and made stationary by a holddown frame. An EL panel for illuminating the liquid crystal panel is mounted behind the liquid crystal panel with a given gap with the EL panel. An EL circuit board holding an EL driver circuit thereon is adhesively bonded to the bottom surface of the EL panel. A shielding plate is mounted on the top surface of the inner circuit board surrounded by the support frame, and is located opposite to the EL panel. The shielding plate consists of a flexible plastic film on which a copper foil is formed. The shielding plate cuts off noise generated from the EL driver circuit. The EL panel is connected with given electrodes on the EL circuit board via lead wires. An electrode on the EL circuit board and an electrode on the circuit board are connected via a contact member. Electric power and control signals are supplied via this contact member.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a display device using a liquid crystal panel.

[0003] 2. Description of the Related Art

[0004] In some of conventional display devices using liquid crystal panels, an EL panel is used as a backlight for a liquid crystal panel a, as shown in FIG. 5. The liquid crystal panel a is connected with electrodes of a circuit board b by an LCD connector. Since the liquid crystal panel a has a large number of pins, area is required for wiring. Usually, the wiring is placed under the liquid crystal panel a. Therefore, an EL driver circuit c for driving the EL panel is not placed under the liquid crystal panel a but in a remote position on the circuit board b. Lead wires d are brought out from the EL panel for connection with the EL driver circuit c.

[0005] Where the EL driver circuit c is placed on the circuit board b remotely from the liquid crystal panel a as mentioned above, space must be secured on the circuit board b for this purpose. This makes the circuit board b bulky. Furthermore, the EL panel is driven with a high driving voltage and so a step-up circuit is employed. This results in considerably severe RF switching noise, which affects the surroundings from the lead wires d. For example, in the case of an instrument for measuring minute electrical currents such as a photometer, the noise may deteriorate the performance of the instrument. Consequently, the panel cannot be placed close to the minute current detection portion or a high-gain amplifier unless any countermeasure is taken. In this way, limitations are placed on the placement of the EL driver circuit. Where the output voltage from this step-up circuit is coupled to the EL panel by the lead wires d, if the step-up circuit is placed remotely from the EL panel, the effect of noise varies according to the manner in which leads are wired. Hence, shielded wires must be used or other countermeasure is necessary. In this manner, there are many problems.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a display device free of the foregoing problems. Accordingly, a display device in accordance with the present invention is characterized in that a liquid crystal panel is spaced a given distance from a circuit board and that an EL panel for illuminating the liquid crystal panel is located behind the liquid crystal panel. Furthermore, an EL circuit board having an EL driver circuit thereon is located behind the EL panel. In this structure, the EL panel and EL circuit board are placed close to each other, and the surroundings are prevented from being adversely affected by noise generated from the EL driver circuit.

[0007] The space between the liquid crystal panel and the circuit board is maintained by a support member. Preferably, the liquid crystal panel is held against the circuit board by a holddown frame. This structure facilitates maintaining the given space between the liquid crystal panel and the circuit board.

[0008] Preferably, a shielding plate is mounted on the circuit board and opposite to the EL panel to cut off noise produced from the EL driver circuit. This structure can prevent the surroundings from being adversely affected by noise.

[0009] It is also desirable that the EL circuit board be electrically connected with the shielding plate. In addition, the EL circuit board is preferably connected via a contact member with power-supply electrodes on the circuit board, the electrodes being exposed from the shielding plate. Moreover, the EL circuit board is preferably connected via the contact member with electrodes used for supplying control signals, the electrodes being exposed from the shielding plate. This structure facilitates making connections and assembling the display device.

[0010] Other objects and features of the invention will appear in the course of the description thereof, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of a display device in accordance with one embodiment of the present invention;

[0012]FIG. 2 is an enlarged cross section taken on line A-A of FIG. 1;

[0013]FIG. 3 is an enlarged cross section taken on line B-B of FIG. 1;

[0014]FIG. 4 is an enlarged cross section of a display device in accordance with another embodiment of the present invention; and

[0015]FIG. 5 is a perspective view of a conventional structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Referring to FIGS. 1-3, there is shown a display device embodying one embodiment of the present invention. This display device has a circuit board 1 on which a liquid crystal panel 2 is placed via a support frame 3 acting as a support member. The liquid crystal panel 2 is mounted in position by a holddown frame 4. The liquid crystal panel 2 comprises two opposite glass plates 21 and 22. A transparent electrode made of ITO is formed on the inner surf ace of each glass plate. An orientation film is formed to cover each transparent electrode. The gap between the electrodes is maintained constant. A liquid crystal material is sealed in between these electrodes. As shown in FIG. 3, the glass substrate 21 has one end portion (right end as viewed in FIG. 3) forming an extraction electrode portion 21 a protruding from the glass substrate 22. The support frame 3 is provided with a hole 3 a opposite to the extraction electrode portion 21 a. A connector 5 passes through this hole 3 a, and is connected with the extraction electrode portion 21 a at its top end. The connector 5 is connected at its bottom end with given electrodes on the circuit board 1. The support frame 3 is provided with a hole 3 b on the side of the other ends (left end as viewed in FIG. 3) of the glass substrates 21 and 22. Liquid crystal support rubber 6 extends through this hole 3 b and holds the liquid crystal panel 2 onto the circuit board 1. As shown in FIG. 2, positioning protrusions 3 c protrude from the bottom surface of the support frame 3 and are fitted in positioning holes (not shown) in the circuit board 1. Thus, the support frame 3 is placed in position on the circuit board 1. Several legs 4 a depend from the holddown frame 4. The bottom ends of the legs 4 a extend through holes 1 a formed in the circuit board 1. These bottom ends have pawls at their front ends. These pawls are anchored to the bottom surface of the circuit board 1.

[0017] An EL panel placement portion for placement of the EL panel 7 is formed on a part of the top surface of the support frame 3. This panel placement portion holds the EL panel 7 to the liquid crystal panel 2 with a given gap. An EL circuit board 8 is adhesively bonded to the bottom surface of the EL panel 7. Circuit elements 8 a for the EL driver circuit are connected. A shielding plate 9 is disposed on the top surface of the circuit board 1 within the interior surrounded by the support frame 3, and is located opposite to the EL panel 7. The shielding plate 9 consists of a plastic film having a copper foil on its top surface and is flexible. Ribs 10 hold down the shielding plate 9. A cushion member 11 is interposed between the tall circuit elements 8 a and the shielding plate 9.

[0018] The EL panel 7 is connected with given electrodes on the EL circuit board 8 via lead wires 7 a. The EL circuit board 8 has electrodes 8 b and 8 c. One end of a contact member 13 is connected with the electrode 8 b. The shielding plate 9 is partially cut away to expose the electrode 1 b on the circuit board 1. The bottom end of the contact member 13 is electrically connected with the exposed electrode 1 b. The electrode 1 b is an electrode for supplying control signals for turning on and off the EL panel and a power supply including ground. The electrode 8 c and the shielding plate 9 are electrically connected via a coil spring 12. The shielding plate 9 is connected with ground of the EL circuit board 8. Therefore, the shielding plate 9 is at the same potential as ground of the board 1.

[0019] Because of this structure, if a high-voltage driving signal is supplied in driving the EL panel 7, noise is cut off and prevented from leaking out, because the EL circuit board 8 is placed inside the support frame 3 and close to the EL panel 7, and because the shielding plate 9 is placed opposite to the EL panel 7.

[0020] Since the driving voltage for the EL panel 7 is high, noise is induced in the lead wire 7 a for supplying the driving signal to the EL panel 7. This lead wire 7 a can be short. Because the shielding plate 9 is disposed inside the support frame 3, the effects of noise on the outside are prevented.

[0021] The EL circuit board 8 uses the contact member 13 to permit electric power and control signals to be supplied via the electrode 8 b to the EL circuit board 8. This makes it unnecessary to solder the EL circuit board 8 and the shielding plate 9 to the circuit board 1. This enhances the assemblability.

[0022] Referring next to FIG. 4, there is shown a display device in accordance with another embodiment of the present invention. This embodiment is similar to the embodiment shown in FIG. 2 except that the coil spring 12 and the contact member 13 are omitted. In particular, the shielding plate 29 is not provided with the cutout to expose the electrode 1 b as shown in FIG. 2. Instead, the shielding plate 29 is so shaped as to cover the whole top surface of the circuit board 1 within the interior surrounded by the support frame 3. One end 29 a of the shielding plate 29 extends outwardly from the support frame 3 and is connected with ground of the circuit board 1. A lead wire 23 is soldered to the electrode 8 b of the EL circuit board 8, and the front end of the lead wire 23 is brought out from the support frame 3. The front end of this lead wire 23 is connected with an electrode on the circuit board 1 in a manner not illustrated. Electric power and control signals are supplied to the EL circuit board 8 via this electrode. Connection with ground is made also via this electrode. Note that like components are indicated by like reference numerals in both FIGS. 2 and 4.

[0023] Connection lines for supplying electric power and control signals via the electrode 8 b produce only a small amount of noise. Therefore, if the lead wire 23 is brought out from the support frame 3, noise will produce little adverse effects.

[0024] Because of the structure described above, the EL panel is close to the EL circuit board holding the EL driver circuit thereon. Effects of noise can be reduced greatly. Since the EL driver circuit is not mounted on the circuit board, the area of the circuit board can be decreased. Consequently, miniaturization can be accomplished. Furthermore, noise can be cut off by mounting the shielding plate. Hence, the effects of noise can be reduced further.

[0025] Additionally, the EL circuit board has a contact member for making an electrical connection. Therefore, the assembly operation can be performed by throwing in parts. Inconsequence, the assemblability can be improved. 

What is claimed is:
 1. A display device comprising: a circuit board; a liquid crystal panel spaced a given distance from said circuit board; an EL panel for illuminating said liquid crystal panel, said EL panel being located behind said liquid crystal panel; and an EL circuit board having an EL driver circuit thereon and located behind said EL panel.
 2. The display device of claim 1 , wherein said liquid crystal panel is supported by a support member such that a given gap is maintained between said liquid crystal panel and said circuit board, and wherein said liquid crystal panel is mounted to said circuit board by a holddown frame.
 3. The display device of claim 1 or 2 , wherein said circuit board has a shielding plate located opposite to said EL panel to cut off noise produced from said EL driver circuit.
 4. The display device of claim 3 , wherein said EL circuit board is electrically connected with said shielding plate.
 5. The display device of claim 4 , wherein said circuit board has a power supply electrode for a power supply and control signal electrodes for supplying control signals, said power supply electrode and said control signal electrodes being exposed from said shielding plate, and wherein said EL circuit board is connected via a contact member with said power supply electrode and said control signal electrodes. 